In automation technology, especially in process automation technology, field devices are often applied, which serve for registering and/or influencing process variables. Serving for registering process variables are sensors, which, for example, are integrated in fill level measuring devices, flow measuring devices, pressure- and temperature measuring devices, pH redox potential measuring devices, conductivity measuring devices, density measuring devices, etc. for registering the corresponding process variables, fill level, flow, pressure, temperature, pH value, redox potential, conductivity, and density. Serving for influencing process variables are actuators, such as, for example, valves or pumps, via which the flow of a liquid in a pipeline section or the fill level in a container can be changed. Referred to as field devices are, in principle, all devices, which are applied near to the process and deliver, or process, process relevant information. In connection with the invention, the terminology, field devices, thus includes also remote I/Os, radio adapters, and, generally, electronic components, which are located at the field level. A large number of such field devices are manufactured and sold by the firm, Endress+Hauser.
Often, radiometry is applied as a measuring method, such as, for example, in the case of a density-or fill level measurement. In the case of a density-and fill level measurement, the measuring method is based on radioactive radiation, preferably gamma radiation, which is emitted from a radiation source and allowed to pass through the medium to be measured. After passage through the medium, the transmitted radiation intensity is measured by a detector unit. By relating the transmitted radiation intensity to original intensity of the radiation source, the density of the medium or the fill level of the medium in the pipe can be deduced. The measuring principle has proved itself especially for density determination of media with high density, which are not purely liquid or gaseous in nature, but, instead, also contain high fractions of solids, such as, for example, muds, slurries, oils or high viscosity media in general.
The determining of the density or the fill level of such media is performed in industrial plants not only in the static state, thus in containers, tanks or other storage facilities, but, instead, also along the transport paths of the respective media in pipelines. In these cases, the measuring arrangement, thus the radiation source as well as the detector unit, is placed on the particular pipe, through which the medium to be measured is led.
In such case, it is necessary to apply the radiation source and the detector unit using a suitable clamping apparatus in such a manner on the pipe, referred to in the following as measuring tube, that the radiation cone of the radiation source is directed toward the measuring tube, and such that the detector unit is located in the radiation cone after passage of the radiation through the measuring tube.
In the case of this configuration, however, it is possible that the radiation cone also reaches regions outside of the measuring tube. This depends firstly on the aperture angle of the radiation cone as well as the diameter of the measuring tube and relates, above all, to the lateral regions between the clamping apparatus and the measuring tube.
During operation and during servicing of the radiometric measuring arrangement, it must, however, be assured that the radiation cone of the radiation source certainly cannot reach maintenance personnel. Thus, it must be prevented that some body part of maintenance personnel gets exposed to radioactive radiation. Especially for clamping holders of the state of the art, this is, however, not automatically a given, since these are constructed, most often, to provide variable aperture angle of the radiation source and to fit different diameters of measuring tube. As a result, a secure structural integration in the clamping holder of protective elements, which make the radiation cone at least laterally inaccessible, is not possible. Rather, the measuring arrangements, which are designed for variable measuring tube diameter, are currently subsequently covered with protective means.